Power efficiency for wireless portable battery-powered devices under a variety of loading conditions is important for extending battery life in such devices. Power amplifiers are often the most power-consuming components in a wireless portable device, and thus their efficiency contributes substantially to the overall power efficiency of the device. Adaptive biasing is a technique that is often deployed in circuit design to obtain a desired amplifier transfer function as a function of its input signal. The adaptive biasing technique tracks the power demands of the system and provides an appropriate gate bias for the amplifier transistors to achieve the desired transfer function and improve the efficiency of the amplifier.